Motor-control system.



G. N. CRABBE.

MOTOR CONTROL SYSTEM.

APPLICATION FILED mm. 21. 1914.

1,245,194. Patented Nov. 6, 1917.

. M61 INVENTOR WITNESSES:

- UNITED STATES PATENT OFFICE.

GEORGE N. CRABIBE, OF CRESSKILL, NEW JERSEY, ASSIGNOR TO OTIS ELEVATORCOM- PANY, OF JERSEY CITY, NEW JERSEY, A CORPORATION OF NEW JERSEY.

MOTOR-CONTROL SYSTEM.

Specification of Letters Patent.

Patented Nov. 6, 191 '7.

Application filed March 21, 1914. Serial No. 826,144.

T '0 all whom it may concern:

Be it known that I, GEORGE N. CRABBE, a citizen of the vUnited States,residing in Cresskill, in the county of Bergen and State of New Jersey,have invented a new and useful Improvement in Motor-Control Systems, ofwhich the following is a specification.

My invention relates to improvements in controlling systems for motors,and is adapted, among other things, automatically to prevent a toosudden reversal of an electric motor.

The invention is adapted to substantially all electric motors which arearranged to- 'have their direction of rotation reversed from time totime, but the same is particularly adapted to an electric elevator orhoist in which the motor is constantly being started, stopped andreversed under load.

I am aware that itis not new, broadly speaking, automatically to preventa too su den reversal of the motor of an electric elevator or hoist butin general the method as used, is objectionable in that it results in asubstantial loss of time.

For example, in a high rise electric elevator, such as one finds in themodern ofiice buildings of a large city, it is very essential that theelevator shall be'operated at high speed and with as little loss of timeas possible in starting, stopping and reversing. In the present instancein particular, and in all other elevator installations to a lesserdegree, an appreciable loss of time is occasioned in case the caroperator centers his controlling switch to stop the car at a landing andthen changes his mind before the car has had time to slow down and stop,and concludes to. continue in the same direction and immediately throwsthe controlling lever into the samerunning position that it was beforehe atte'mpted to stop. Under this condition, the

automatic means for preventing a too sudden reversal will prevent theoperator from closing a circuit to the motor until after the latter hassubstantially come to rest, whereas it is entirely feasible to permitthe operator a ain to close a circuit to the motor immediate y it hasbeen opened, providing of course the motor circuit is closed in' thesame direction as before and not in a reverse direction tending toeffect a sudden reversal.

My invention provides a simple, practical and eflicient means forpreventing a too sudbefore without having to wait until themotor hassubstantially come to rest or had its speed materially reduced, therebyeffecting an appreciable saving of time, which, as above pointed out,'ismost desirable. Figure 1 of the accompanying drawing is a diagrammaticrepresentation of an electric elevator system containing an embodimentof my invention in a simple form; Fig. 2 is a detail view of anadjustable relay.

Referring to the drawing, an electric motor M is adapted to be started,stopped and reversed by means of the reversing switches R and R whichare controlled by a switch S located in the elevator car or otherconvenient place. The reversing switches are preferably mechanicallyinterlocking by means of a lever 10 having a pin and slot connectionwith each reversing switch, so

that it isimpossible for both switches simultaneously to be closed or intheir extreme lowermost position. The motor field winding is representedby the letter F while an accelerating magnet A is arranged automaticallyto short circuit the starting resistance B in a plurality of steps inaccordance with the load on the motor in a well known way. A pair ofrelays 20 and 30 have their windings connected in series across themotor armature and hence operate according to the varyingcounter-electro-motive force of the motor and consequently the speed ofthe motor. i

The operation of the controlling system is as follows: Assuming theparts of the apparatus in the position shown, the operator first movesthe lever of switch S, say for exampleto the right, into electricalenagement with the contact 11. A circuit is now closed from the main,through the .magnet winding 12 of reversing switch R,

contacts 13 of relay 30, contact 11 of switch S and to the main. Thecore 14 of re-- contacts 17 of switch R, armature brush 19 to brush 21,contacts 18 of switch R,

' through the starting resistance B and to the main. The motor nowstarts to rotate and as its speed increases its counterelectro-motiveforce rises until the accelerating magnet is enabled to close one of itscontacts. This results in a short circuiting of a portion of thestarting resistance followed by a further increase in motor speed andattendant counter-electro-motive force, and the accelerating magnet isthus enabled successively to short circuit the entire startingresistance in a plurality of steps and the motor quickly runs up to fullnormal speed. It will be noted that the magnet winding of relay 30 is atthis time short-circuited by the reversing switch contacts 17 and willnot be operated, consequently the magnet winding of relay 20 receivescurrent at the full potential of the motor armature, and, after thispotential has reached a predetermined amount as the motor acceleratesin. starting, the relay 20 will raise its core and thereby open circuitthe contacts 22. These latter contacts are connected in the circuit ofthe winding of reversing switch R, hence it follows that it becomesimpossible to raise the reversing switch R while the motor is rotatingat an appreciable speed with the reversing switch R in closed position.If the operator attempts suddenly to reverse the motor by throwing thecontrolling switch S from one side to the other, it will 35 be seen thatthis operation merely opens the circuit of the magnet of switch It atthe contact 11 but does not close a circuit to the other reversingswitch R since the relay '20 will remain in raised position until thepoential and speed of the motor undergoes a substantial reduction oruntil the motor ractically comes to rest. As soon as the re-- ay 20 isenabled to drop its core so as again to short circuit the contacts 22, acircuit may then be closed to the magnet of the reversing switch It andthe motor reversed.

If the controlling switch S be moved ofi of the contact 11 to stop themotor while the latter is running at full s eed, and the operatorchanges his mind an at once moves his switch lever back onto contact 11for the purpose of continuing the trip, the reversing switch R willfirst simultaneously open the )motor and. the accelerating magnetcircuits 5 and immediately close sald circuits before the motor has hadtime substantially to reduce its speed. The starting resistance is ofcourse reinsertedin the motor circuit butis rapidly cut out again,ro'viding the speed of the motor has not con materially reduced. Hencethe motor is protected against a sudden rush of current when the motorcircuit is'temporarily interrupted. -Whileit' is most desirable andnecessary to wait for the motor to slow down before the operator caneffect a reversal of the motor so as to prevent a sudden rush ofcurrent, and to prevent all shocks and jars to the motor and 113sconnected load, such as the elevator car, it is also most desirable toenable the operator to open the motor circuit and again close it in thesame direction without having to wait for the counter-electro-motiveforce and s eed of the motor to die out. This results in a substantialsaving of time, which, as before pointed out, is-of decided advantage inthe great majority of cases and particularly so in the case of electricelevators.

The operation of the system in a reverse direction is similar to thatjust described; the relay 30 .being automatically operated to prevent atoo sudden reversal of the motor by the closing of the reversing switchR while the reversing switch R may be opened and closed wheneverdesired.

I prefer to construct the relays 20 and 30 as shown in Fig. 2, in whichthe screw plug 23 may be moved so as to vary the air gap between it andthe magnet core 24, and in this manner the relay may be set or adjustedto operate on a current of a predetermined potential. In other words therelay may be adjusted so as to open circuitits contacts as soon as themotor commences to generate an appreciable counter-electro-motive force,or if desired the relay will not operate until the motor has run up to,say, one quarter speed, or more. The nuts 25, are threaded on the core24 and may be adjusted so that the lift of the core may be varied sothat the latter will drop at a predetermined motor potential and shortcircuit the relay contacts. other suitable resilient material ispreferably located on the core as shown, so as to act in the nature of acushioning device or buffer, and thereby enable the relays to operatenoiselessly.

A- washer 26 of leather, rubber or While I have described my inventionwith when, the power circuit to the motor is opened at the reversingswitches since the arrangement and electrical connections, for the sameare wellknown in the art and form no part page of the invention.

. I desire not to" be limited to the precise construction andarrangement of parts herein disclosed, since it is obvious that oneskilled in the art could readily make changes and alterations thereinwithout'depermitting the energization of the other electromagnet whilethe motor is rotating.

2. The combination with an electric motor, of electromagnetic reversingswitches therefor, a separate relay for controlling the operatingcircuit of each reversing switch, one relay operable at a predeterminedspeed of the motor, while the other relay will not operate until themotor is substantially at rest.

3. The combination with an electric motor, of electromagnetic reversingswitches therefor, a separate relay for controlling the operatingcircuit of each reversing switch,

means controlled by the motor for effecting the operation of one relay,and means for preventing the operation of the other relay until themotor is substantially at rest.

4. The combination with an electric motor, of electromagnetic reversingswitches therefor, a separate relay for controlling the operatingcircuit of each reversing switch, means controlled by the motor foreffecting the operation of one relay, and means controlled by one of thereversing switches for preventing the operation of the other relay untilthe motor is substantially at rest.

5. The combination with an electric motor, of a pair of electromagneticreversing switches. therefor, a separate relay controlling the operatingcircuit of each reversing switch,means for controllin said relays inaccordance with the speed 0 the motor, and

means dependent upon the operation of a reversing switch for preventingthe operation of one of said relays whereby a circuit may beclosed tothe magnet of one revers ing switch at any speed of the motor butpreventing the operation of the other reversing switch until the motorsubstantially comes to rest.

6. In a system of motor control, the combination of a motor, reversingswitches, an operating circuit for each switch, and a relay for eachoperating circuit permanently connected to the motor controlled by thespeed of the motor for maintaining but one of the said operatingcircuits open until such speed is substantially reduced. l

7. In a system of motor control, the combination of a motor, reversingswitches, an operating circuit for each switch, a separate relaycontrollingeach operating circuit, the windings of said relays beingconnected in series across the motor armature, means for effecting theoperation of one relay to open the operating circuit of one reversingswitch to prevent a sudden reversal of the motor, and means for shortcircuiting the winding of the other relay so as to permit closing theoperating circuit of the other reverslng switch. 1

8. In a system of motor control, the combination of a motor, reversingswitches, an operating circuit for each switch, a separate relaycontrolling each operating .circuit, means for closing either operating01?- cuit through the contacts of a relay, and means controlled by themotor for effecting the operation of but one of saidrelays.

9. In a system of motor control, the combination-of a motor, reversingswitches, an operating circuit for each switch, a separate relaycontrolling each operating circult,

means for closing either operating circuit' through the contacts of arelay, means controlled by the motor for effecting the oper tion of butone of said relays, and means for adjusting said, relays so that theywill operate at a predetermined potential both GEORGE N. CRABBE.

Q Witnesses WALTER C. STRANG, JAMES G. BETHELL.

